Cambridge, MA-based Aveo Oncology was fired up early this year when it hit the main goal of its pivotal clinical trial with a kidney cancer drug. But today some new questions have emerged about how much benefit its drug is offering to patients, which sent the company’s stock down more than 25 percent. Aveo (NASDAQ: AVEO) said today in its quarterly financial report that the FDA has “expressed concern” about new results from a trial called TIVO-1 which show that 81 percent of patients who were randomly assigned to get Bayer and Onyx Pharmaceuticals’ sorafenib (Nexavar) were alive after one year, compared with 77 percent who got Aveo’s tivozanib. Aveo cautioned that not enough deaths have occurred in the entire trial of 517 patients to make this a final result, and median survival time for the two groups can’t yet be calculated.